1. Field of the Invention
This invention relates to a recording/reproducing apparatus which includes a PG yoke for detecting timing signals for recording or reproducing apparatus which includes a PG yoke for detecting timing signals for recording or reproducing signals from a magnetic recording medium which removes noise from the PG signal to ensure correct recording timing.
2. Description of the Background Art
In a still video system which records still video signals on a magnetic disc and reproduces video signals from the magnetic disc, a rotational position detection signal of a rotating magnetic disc is used in a servo system for a magnetic disc drive motor and in the head selection for frame recording. The rotational position detection signal, or so-called a PG signal, is obtained when a PG yoke provided on the magnetic disc passes over predetermined position as the magnetic disc rotates.
FIG. 8 is a circuit diagram showing ON/OFF control of the recording signal in the recording operation, as an example of the use of the PG signal. In FIG. 8, numeral 1 indicates a PG sensor, numeral 2 indicates an amplifier, numeral 3 indicates a hysteresis circuit, numeral 4 indicates a monomultivibrator for adjusting the PG switching position, numeral 5 indicates a D flip-flop for obtaining a Q output of a recording enable signal using the output of the monomultivibrator 4 as a clock, and numeral 6 indicates a recording switch controlled by the output of the D flip-flop 5. A recording system comprises CCD imaging device 7 a signal processing circuit 8 for the video signal obtained, a Y-FM modulator 9 and a chroma FM modulator 10, a recording amplifier 11, and a magnetic head 12. The recording switch 6 is disposed between the recording amplifier 11 and the head 12, which uses the PG signal to perform ON/OFF control of recording.
However, a signal from the PG sensor 1 (called a first signal) and an output signal (called a second signal) of the monomultivibrator 4, which is obtained by waveform-shaping the first signal, may sometimes contain magnetic or electrostatic noise or noise from other causes, as shown in FIG. 9. Since this noise input to the D flip-flop the second signal at the clock terminal and the recording enable signal (called a RECEN signal) input at a D terminal combine to form the O output, for example, the switch 6 is switched at a period shorter than the normal period indicated by the broken lines in FIG. 9. According, the video signal is not recorded at a correct timing, resulting in an unrecorded part of the video signal. In addition, in frame reproduction, for example, there is a possibility of switching the inner-side and outer-side heads at a part other than the proximity of the vertical sync signal, resulting in a disturbed or skewed image on the television screen.